In an SOFC, to generate electricity by the electrochemical reaction of hydrogen and oxygen, a gas rich in hydrogen is fed to an anode of the SOFC. There is known an SOFC system including a reformer for reforming raw material for producing hydrogen such as a hydrocarbon fuel to produce hydrogen.
Reforming type includes partial oxidation reforming (POX), auto-thermal reforming (ATR) and steam reforming (SR). For example, taking up methane as an example of the raw material for producing hydrogen, in the steam reforming, methane is decomposed to produce hydrogen by the reaction represented by CH4+H2O→CO+3H2, and in the partial oxidation reforming, methane is decomposed to produce hydrogen by the reaction represented by CH4+1/2O2→CO+2H2. In the auto-thermal reforming, both of these reactions take place.
With the steam reforming, compared to the other reforming, a hydrogen concentration in a reformed gas produced is higher, and when it is applied to an SOFC system, higher electric generation efficiency is achieved. Since it has such advantage, an SOFC system including a steam reformer and an SOFC which uses the reformed gas produced by the steam reformer as a fuel has been developed.
Such an SOFC system is described, for example, in Patent Document 1.    Patent Document 1: Japanese Patent Laid-Open No. 2003-272690